“V-type” internal combustion engine (ICE) assemblies are traditionally defined by an engine block having a pair of outwardly angled cylinder banks with inside walls that define an interbank valley therebetween. Each cylinder bank of a typical V-type over-head valve ICE defines a cylinder bore having a piston reciprocally movable therein. The piston and cylinder bore cooperate with a portion of a cylinder head to form a variable volume combustion chamber. The cylinder head defines intake ports through which air, provided by an intake manifold, is selectively introduced into the combustion chamber. Additionally, the cylinder head defines exhaust ports through which exhaust gases or products of combustion are selectively evacuated from the combustion chamber. Normally, an exhaust manifold is affixed to the cylinder head, by bolting or other fastening means, such that the exhaust manifold communicates with each exhaust port to carry the exhaust gases from the ICE to a vehicular exhaust aftertreatment system for subsequent release to the atmosphere.
In-cylinder emissions reduction devices, such as exhaust gas recirculation (EGR) systems, are also included in many current engine assemblies in order to curtail the amount of NOx and other pollutants from the exhaust gas released into the atmosphere. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. Recirculation affects the engine's combustion process in three primary ways. First, there is a dilution effect caused by the reduction in the concentration of oxygen in intake air. Second, there is a thermal effect caused by increasing the specific heat capacity of each charge. Third, there is a chemical effect which results from the dissociation of CO2 and water vapor during combustion. EGR can be achieved by either recirculating some of the exhaust leaving the engine back into the engine, which is known as external EGR, or by retaining a fraction of the exhaust gas—i.e., gas never leaves the engine, which is known as internal EGR. Major exhaust gas constituents that are “recirculated” include N2, CO2, water vapor, and partially burned hydrocarbons.
Some modern ICEs employ a mechanical supercharging device such as a turbocharger, which is short for turbine driven, forced induction supercharger. Most turbochargers include a turbine portion and a compressor portion. The turbine portion has a turbine housing that is in fluid communication at an inlet end with the engine exhaust manifold. The turbine housing receives exhaust gases from the exhaust manifold, and redirects the exhaust stream to spin a turbine blade. The turbine blade is rigidly mounted to a compressor blade for unitary rotation therewith. As the compressor blade spins, ambient air is compressed within a compressor housing; the compressed air is subsequently introduced to the intake manifold to increase the volumetric efficiency of the ICE.
To maximize the performance of the turbocharger, the turbine housing is typically located as close to the exhaust port as possible so that heat energy from the flowing exhaust stream that might otherwise be used to spin the turbine blade is not wasted through radiation to the atmosphere. Consequently, when a turbocharger is attached to a V-type ICE, the turbocharger is often mounted immediately adjacent to the valley, between the two cylinder banks of the engine block, to minimize the distance of travel of the exhaust stream, and to maximize use of the space between the banks. In this type of arrangement, the turbocharger is often surrounded by a protective jacket (commonly referred to as a valley shield or acoustic pad) in order to minimize undesirable radiation of heat and noise generated by engine components, such as, for example, the exhaust manifold, and also to maintain the energy content of the exhaust gases.